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Shareholder Report
 6 Months Ended
May 31, 2024
USD ($)
Holdings
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Northern Institutional Funds
Entity Central Index Key 0000710124
Entity Investment Company Type N-1A
Document Period End Date May 31, 2024
Line Graph [Table Text Block]
LIQUID ASSETS PORTFOLIO (NILAP)  
Shareholder Report [Line Items]  
Fund Name LIQUID ASSETS PORTFOLIO
Class Name LIQUID ASSETS PORTFOLIO
Trading Symbol NILAP
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Liquid Assets Portfolio (the “Portfolio”) for the period of December 1, 2023 to May 31, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Portfolio at
ntam.northerntrust.com/united-states/institutional/institutional-liquid-assets-portfolio#literature
. You can also request this information by contacting us at 800-637-1380.
Additional Information Phone Number 800-637-1380
Additional Information Website ntam.northerntrust.com/united-states/institutional/institutional-liquid-assets-portfolio#literature
Expenses [Text Block]
What were the Portfolio costs for the last six months?
(Based on a hypothetical $10,000 investment)
Fund
Costs of a $10,000 investment
1
Costs paid as a percentage of a $
10,000
investment
1,2
LIQUID ASSETS PORTFOLIO
$
2		0.03
%
1
   
Reflects applicable expense reimbursements and fee waivers.
2
   
Expense ratio is expressed on an annualized basis.
Expenses Paid, Amount $ 2 [1]
Expense Ratio, Percent 0.03% [1],[2]
Performance Past Does Not Indicate Future [Text] The Portfolio's past performance is not a good predictor of the Portfolio's future performance.
Line Graph [Table Text Block]
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns
1 year
5 years
10 years
LIQUID ASSETS PORTFOLIO5.49
%
2.16
%
1.53
%
No Deduction of Taxes [Text Block] The graph and table above do not reflect the deduction of taxes that a shareholder would pay on Portfolio distributions or redemption of Portfolio shares.
Updated Performance Information Location [Text Block] Performance data current to the most recent month-end is available at
ntam.northerntrust.com/united-states/institutional/institutional-liquid-assets-portfolio#performance
.
Net Assets $ 1,768,541,000
Holdings Count | Holdings 58
Additional Fund Statistics [Text Block]
KEY PORTFOLIO STATISTICS
Portfolio net assets (in thousands)
$
1,768,541
Total number of portfolio holdings58
Holdings [Text Block]
TYPE OF SECURITY AS A % OF NET ASSETS
U.S. Government Agencies19.9
%
U.S. Government Obligations13.4
%
Repurchase Agreements70.3
%
Figures in the above table may not sum to 100% due to the exclusions of other asset and liabilities.
U.S. GOVERNMENT PORTFOLIO (SHARES/BNGXX)  
Shareholder Report [Line Items]  
Fund Name U.S. GOVERNMENT PORTFOLIO
Class Name SHARES
Trading Symbol BNGXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the U.S. Government Portfolio (the “Portfolio”) for the period of December 1, 2023 to May 31, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Portfolio at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
. You can also request this information by contacting us at 800-637-1380.
Additional Information Phone Number 800-637-1380
Additional Information Website ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
Expenses [Text Block]
What were the Portfolio costs for the last six months?
(Based on a hypothetical $10,000 investment)
Portfolio (Class)
Cost of $10,000 Investment
1
Costs paid as a percentage of a $10,000 investment
1,2
U.S. GOVERNMENT PORTFOLIO
(SHARES/BNGXX)
$
13		0.25
%
1
Reflects applicable expense reimbursements and fee waivers.
2
Expense ratio is expressed on an annualized basis.
Expenses Paid, Amount $ 13 [1]
Expense Ratio, Percent 0.25% [1],[2]
Performance Past Does Not Indicate Future [Text] The Portfolio's past performance is not a good predictor of the Portfolio's future performance.
Average Annual Return [Table Text Block]
Average Annual Total Returns
1 year
5 years
10 years
U.S. GOVERNMENT PORTFOLIO (SHARES/BNGXX)5.24
%
1.96
%
1.31
%
No Deduction of Taxes [Text Block] The graph and table above do not reflect the deduction of taxes that a shareholder would pay on Portfolio distributions or redemption of Portfolio shares.
Updated Performance Information Location [Text Block] Performance data current to the most recent month-end is available at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#performance
.
Net Assets $ 20,836,704,000
Holdings Count | Holdings 110
Additional Fund Statistics [Text Block]
KEY PORTFOLIO STATISTICS
Portfolio net assets (in thousands)
$
20,836,704
Total number of portfolio holdings110
Holdings [Text Block]
TYPE OF SECURITY AS A % OF NET ASSETS
U.S. Government Agencies28.0
%
U.S. Government Obligations14.2
%
Repurchase Agreements57.1
%
Figures in the above table may not sum to 100% due to the exclusions of other asset and liabilities.
U.S. GOVERNMENT SELECT PORTFOLIO (SERVICE SHARES/BSCXX)  
Shareholder Report [Line Items]  
Fund Name U.S. GOVERNMENT SELECT PORTFOLIO
Class Name SERVICE SHARES
Trading Symbol BSCXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the U.S. Government Select Portfolio (the “Portfolio”) for the period of December 1, 2023 to May 31, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Portfolio at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
. You can also request this information by contacting us at 800-637-1380.
Additional Information Phone Number 800-637-1380
Additional Information Website ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
Expenses [Text Block]
What were the Portfolio costs for the last six months?
(Based on a hypothetical $10,000 investment)
Portfolio (Class)
Cost of $10,000 Investment
1
Costs paid as a percentage of a $10,000 investment
1,2
U.S. GOVERNMENT SELECT PORTFOLIO
(SERVICE SHARES/BSCXX)
$
9		0.17
%
1
Reflects applicable expense reimbursements and fee waivers.
2
Expense ratio is expressed on an annualized basis.
Expenses Paid, Amount $ 9 [1]
Expense Ratio, Percent 0.17% [1],[2]
Performance Past Does Not Indicate Future [Text] The Portfolio's past performance is not a good predictor of the Portfolio's future performance.
Line Graph [Table Text Block]
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns
1 year
5 years
10 years
U.S. GOVERNMENT SELECT PORTFOLIO (SERVICE SHARES/BSCXX)5.31
%
1.99
%
1.35
%
No Deduction of Taxes [Text Block] The graph and table above do not reflect the deduction of taxes that a shareholder would pay on Portfolio distributions or redemption of Portfolio shares.
Updated Performance Information Location [Text Block] Performance data current to the most recent month-end is available at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#performance
.
Net Assets $ 27,755,642,000
Holdings Count | Holdings 111
Additional Fund Statistics [Text Block]
KEY PORTFOLIO STATISTICS

Portfolio net assets (in thousands)
$
27,755,642
Total number of portfolio holdings111
Holdings [Text Block]
TYPE OF SECURITY AS A % OF NET ASSETS
U.S. Government Agencies30.7
%
U.S. Government Obligations14.3
%
Repurchase Agreements51.7
%
Figures in the above table may not sum to 100% due to the exclusions of other asset and liabiliti
es.
U.S. GOVERNMENT SELECT PORTFOLIO (SHARES/BGSXX)  
Shareholder Report [Line Items]  
Fund Name U.S. GOVERNMENT SELECT PORTFOLIO
Class Name SHARES
Trading Symbol BGSXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the U.S. Government Select Portfolio (the “Portfolio”) for the period of December 1, 2023 to May 31, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Portfolio at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
. You can also request this information by contacting us at 800-637-1380.
Additional Information Phone Number 800-637-1380
Additional Information Website ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
Expenses [Text Block]
What were the Portfolio costs for the last six months?
(Based on a hypothetical $10,000 investment)
Portfolio (Class)
Cost of $10,000 Investment
1
Costs paid as a percentage of a $10,000 investment
1,2
U.S. GOVERNMENT SELECT PORTFOLIO
(SHARES/BGSXX)
$
9		0.17
%
1
Reflects applicable expense reimbursements and fee waivers.
2
Expense ratio is expressed on an annualized basis.
Expenses Paid, Amount $ 9 [1]
Expense Ratio, Percent 0.17% [1],[2]
Performance Past Does Not Indicate Future [Text] The Portfolio's past performance is not a good predictor of the Portfolio's future performance.
Line Graph [Table Text Block]
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns
1 year
5 years
10 years
U.S. GOVERNMENT SELECT PORTFOLIO (SHARES/BGSXX)5.31
%
1.99
%
1.35
%
No Deduction of Taxes [Text Block] The graph and table above do not reflect the deduction of taxes that a shareholder would pay on Portfolio distributions or redemption of Portfolio shares.
Updated Performance Information Location [Text Block] Performance data current to the most recent month-end is available at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#performance
.
Net Assets $ 27,755,642,000
Holdings Count | Holdings 111
Additional Fund Statistics [Text Block]
KEY PORTFOLIO STATISTICS
Portfolio net assets (in thousands)
$
27,755,642
Total number of portfolio holdings111
Holdings [Text Block]
TYPE OF SECURITY AS A % OF NET ASSETS
U.S. Government Agencies30.7
%
U.S. Government Obligations14.3
%
Repurchase Agreements51.7
%
Figures in the above table may not sum to 100% due to the exclusions of other asset and liabilities.
U.S. GOVERNMENT SELECT PORTFOLIO (SIEBERT WILLIAMS SHANK SHARES/WCGXX)  
Shareholder Report [Line Items]  
Fund Name U.S. GOVERNMENT SELECT PORTFOLIO
Class Name SIEBERT WILLIAMS SHANK SHARES
Trading Symbol WCGXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the U.S. Government Select Portfolio (the “Portfolio”) for the period of December 1, 2023 to May 31, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Portfolio at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
. You can also request this information by contacting us at 800-637-1380.
Additional Information Phone Number 800-637-1380
Additional Information Website ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
Expenses [Text Block]
What were the Portfolio costs for the last six months?
(Based on a hypothetical $10,000 investment)
Portfolio (Class)
Cost of $10,000 Investment
1
Costs paid as a percentage of a $10,000 investment
1,2
U.S. GOVERNMENT SELECT PORTFOLIO
(SIEBERT WILLIAMS SHANK SHARES/WCGXX)
$
9		 0.17
%
1
Reflects applicable expense reimbursements and fee waivers.
2
Expense ratio is expressed on an annualized basis.
Expenses Paid, Amount $ 9 [1]
Expense Ratio, Percent 0.17% [1],[2]
Performance Past Does Not Indicate Future [Text] The Portfolio's past performance is not a good predictor of the Portfolio's future performance.
Line Graph [Table Text Block]
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns
1 year
5 years
Since
Inception
U.S. GOVERNMENT SELECT PORTFOLIO (SIEBERT WILLIAMS SHANK SHARES/WCGXX) 5.31
%
 1.99
%
 1.39
%
Performance Inception Date Sep. 15, 2014
No Deduction of Taxes [Text Block] The graph and table above do not reflect the deduction of taxes that a shareholder would pay on Portfolio distributions or redemption of Portfolio shares.
Updated Performance Information Location [Text Block] Performance data current to the most recent month-end is available at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#performance
.
Net Assets $ 27,755,642,000
Holdings Count | Holdings 111
Additional Fund Statistics [Text Block]
KEY PORTFOLIO STATISTICS
Portfolio net assets (in thousands)
$
27,755,642
Total number of portfolio holdings 111
Holdings [Text Block]
TYPE OF SECURITY AS A % OF NET ASSETS
U.S. Government Agencies 30.7
%
U.S. Government Obligations 14.3
%
Repurchase Agreements 51.7
%
Figures in the above table may not sum to 100% due to the exclusions of other asset and liabilities.
TREASURY PORTFOLIO (PREMIER SHARES/NTPXX)  
Shareholder Report [Line Items]  
Fund Name TREASURY PORTFOLIO
Class Name PREMIER SHARES
Trading Symbol NTPXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Treasury Portfolio (the “Portfolio”) for the period of December 1, 2023 to May 31, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Portfolio at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
. You can also request this information by contacting us at 800-637-1380.
Additional Information Phone Number 800-637-1380
Additional Information Website ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
Expenses [Text Block]
What were the Portfolio costs for the last six months?
(Based on a hypothetical $10,000 investment)
Portfolio (Class)
Cost of $10,000 Investment
1
Costs paid as a percentage of a $10,000 investment
1,2
TREASURY PORTFOLIO
(PREMIER SHARES/NTPXX)
$
10		 0.20
%
1
Reflects applicable expense reimbursements and fee waivers.
2
Expense ratio is expressed on an annualized basis.
Expenses Paid, Amount $ 10 [1]
Expense Ratio, Percent 0.20% [1],[2]
Performance Past Does Not Indicate Future [Text] The Portfolio's past performance is not a good predictor of the Portfolio's future performance.
Line Graph [Table Text Block]
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns
1 year
5 years
Since
Inception
TREASURY PORTFOLIO (PREMIER SHARES/NTPXX) 5.28
%
 1.97
%
 1.70
%
Performance Inception Date Aug. 01, 2016
No Deduction of Taxes [Text Block] The graph and table above do not reflect the deduction of taxes that a shareholder would pay on Portfolio distributions or redemption of Portfolio shares
Updated Performance Information Location [Text Block] Performance data current to the most recent month-end is available at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#performance
.
Net Assets $ 82,131,465,000
Holdings Count | Holdings 78
Additional Fund Statistics [Text Block]
KEY PORTFOLIO STATISTICS
Portfolio net assets (in thousands)
$
82,131,465
Total number of portfolio holdings 78
Holdings [Text Block]
TYPE OF SECURITY AS A % OF NET ASS
ETS
U.S. Government Obligations 49.4
%
Repurchase Agreements 50.4
%
Figures in the above table may not sum to 100% due to the exclusions of other asset and liabilities.
TREASURY PORTFOLIO (SHARES/NITXX)  
Shareholder Report [Line Items]  
Fund Name TREASURY PORTFOLIO
Class Name SHARES
Trading Symbol NITXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Treasury Portfolio (the “Portfolio”) for the period of December 1, 2023 to May 31, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Portfolio at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
. You can also request this information by contacting us at 800-637-1380.
Additional Information Phone Number 800-637-1380
Additional Information Website ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
Expenses [Text Block]
What were the Portfolio costs for the last six months?
(Based on a hypothetical $10,000 investment)
Portfolio (Class)
Cost of $10,000 Investment
1
Costs paid as a percentage of a $10,000 investment
1,2
TREASURY PORTFOLIO
(SHARES/NITXX)
$
8		0.15
%
1
Reflects applicable expense reimbursements and fee waivers.
2
Expense ratio is expressed on an annualized basis.
Expenses Paid, Amount $ 8 [1]
Expense Ratio, Percent 0.15% [1],[2]
Performance Past Does Not Indicate Future [Text] The Portfolio's past performance is not a good predictor of the Portfolio's future performance.
Line Graph [Table Text Block]
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns
1 year
5 years
10 years
TREASURY PORTFOLIO (SHARES/NITXX)5.33
%
2.01
%
1.38
%
No Deduction of Taxes [Text Block] The graph and table above do not reflect the deduction of taxes that a shareholder would pay on Portfolio distributions or redemption of Portfolio shares
Updated Performance Information Location [Text Block] Performance data current to the most recent month-end is available at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#performance
.
Net Assets $ 82,131,465,000
Holdings Count | Holdings 78
Additional Fund Statistics [Text Block]
KEY PORTFOLIO STATISTICS
Portfolio net assets (in thousands)
$
82,131,465
Total number of portfolio holdings78
Holdings [Text Block]
TYPE OF SECURITY AS A % OF NET ASSETS
U.S. Government Obligations49.4
%
Repurchase Agreements50.4
%
Figures in the above table may not sum to 100% due to the exclusions of other asset and liabilities.
TREASURY PORTFOLIO (SIEBERT WILLIAMS SHANK SHARES/SWSXX)  
Shareholder Report [Line Items]  
Fund Name TREASURY PORTFOLIO
Class Name SIEBERT WILLIAMS SHANK SHARES
Trading Symbol SWSXX
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about the Treasury Portfolio (the “Portfolio”) for the period of December 1, 2023 to May 31, 2024.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Portfolio at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
. You can also request this information by contacting us at 800-637-1380.
Additional Information Phone Number 800-637-1380
Additional Information Website ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#literature
Expenses [Text Block]
Portfolio (Class)
Cost of $10,000 Investment
1
Costs paid as a percentage of a $10,000 investment
1,2
TREASURY PORTFOLIO
(SIEBERT WILLIAMS SHANK SHARES/SWSXX)
$
8		0.15
%
1
Reflects applicable expense reimbursements and fee waivers.
2
Expense ratio is expressed on an annualized basis.
Expenses Paid, Amount $ 8 [1]
Expense Ratio, Percent 0.15% [1],[2]
Performance Past Does Not Indicate Future [Text] The Portfolio's past performance is not a good predictor of the Portfolio's future performance.
Line Graph [Table Text Block]
Fund Performance - Growth of 10K
Average Annual Return [Table Text Block]
Average Annual Total Returns
1 year
5 years
10 years
TREASURY PORTFOLIO (SIEBERT WILLIAMS SHANK SHARES/SWSXX)5.33
%
2.01
%
1.38
%
No Deduction of Taxes [Text Block] The graph and table above do not reflect the deduction of taxes that a shareholder would pay on Portfolio distributions or redemption of Portfolio shares.
Updated Performance Information Location [Text Block] Performance data current to the most recent month-end is available at
ntam.northerntrust.com/united-states/institutional/strategies/cash/northern-institutional-funds#performance
.
Net Assets $ 82,131,465,000
Holdings Count | Holdings 78
Additional Fund Statistics [Text Block]
KEY PORTFOLIO STATISTICS
Portfolio net assets (in thousands)
$
82,131,465
Total number of portfolio holdings78
Holdings [Text Block]
TYPE OF SECURITY AS A % OF NET ASSETS
U.S. Government Obligations49.4
%
Repurchase Agreements50.4
%
Figures in the above table may not sum to 100% due to the exclusions of other asset and liabilities.
[1] Reflects applicable expense reimbursements and fee waivers.
[2] Expense ratio is expressed on an annualized basis.